When the taxable payment covers a period of less than one month, the rate of the tax shall be that which is applicable to the corresponding monthly payment.
When the taxable payment covers a period of more than one month the tax shall be calculated as if this payment had been spread evenly over the months to which it relates.
Corrective payments not related to the month during which they are paid shall be subject to the tax to which they would have been subject had they been made at the proper time.